The invention relates to a return air blocking device in the nature of a check valve mechanism for use in ventilation systems for the interior of motor vehicles. The device comprises a housing attachable in a support panel aperture and connected with at least one flap-type valve element which in the closed position rests against a grating.
It is known in the present state of the art to design a return air blocking device comprising an exterior housing, an inner frame, and a valve element related in such manner that the exterior housing and the inner frame are positioned in each other in nest-like fashion. The elements are joined with one another via clip connections. These clip connections of the inner frame serve simultaneously for fastening the entire unit in a support aperture.
Prior art is also known in which a return air blocking device for motor vehicles is designed for the elimination of flutter noises produced by the flap valve element. The device uses several hook-like bridges arranged in a way such that at the level at which the fluttering begins, the flap valve element touches the free tip of at least one of the bridges (German Petty Patent 37 09 224). With increasing air velocity through the device, the valve element bends at the lower edge and molds itself to the bridges and is held in angular position. This known design is expensive to construct and, further, the entire unit exhibits inadequate stability.
The suggestion has already been made to construct a return air blocking device in such manner that the inner frame is set into the front of the housing (German Printed Patent Application P 40 02 052.5).
In contrast thereto, it is the objective of the present invention to design a return air blocking device of the initially cited type in such manner that there will result a significant simplification in construction and a reduction in the number of individual parts.